The present invention relates to the transfer of articles, such as semiconductor wafers, and more particularly to a vertically integrated processing system and a method and apparatus for transferring semiconductor wafers in such a vertically integrated system.
In semiconductor substrate or wafer processing, electrostatic chucks (E-chucks) are typically used to maintain a wafer in position on a pedestal (or other wafer support) during wafer processes such as sputtering, other physical vapor deposition (PVD) processes, chemical vapor deposition (CVD) processes, etching, or ion implantation. The E-chuck replaces prior art clamping rings, which are placed about the periphery of the wafer to hold it down on the pedestal. An advantage of the E-chuck over a clamping ring is that it does not create the stresses caused by the clamp ring engaging and putting pressure on the edges of the wafer, and it does not overhang the wafer edge and thereby reduce the real estate on the wafer available for deposition as is caused by the inner perimeter of the clamping ring overhanging the wafer.
A typical wafer processing apparatus includes one or more central transfer chambers surrounded by a number of pre-processing, processing and post-processing chambers located on the same processing plane. A critical consideration in semiconductor wafer processing is the footprint of the processing apparatus. During processing, the machines must normally be located in a clean room, which can cost upwards of several thousand dollars per square foot. This is a particular concern in machines designed to process 12xe2x80x3 (300 mm) wafers. Therefore, there exists a need for a semiconductor processing apparatus that can maintain maximum process and wafer throughput while maintaining as small a foot print as possible.
The present invention is an apparatus and method for transferring an article, such as a semiconductor wafer, in both a theta axis and a z-axis, to maintain maximum process and wafer throughput, while minimizing the footprint of the processing machine. The invention utilizes the concept of xe2x80x9cvertical integrationxe2x80x9d to maximize the use of process slots and minimize the machine foot print.
According to one aspect of the present invention, an apparatus is provided for transferring an article both in a z-axis and a theta axis. The apparatus according to this aspect of the invention comprises an electrostatic pick-up for engaging the article, preferably at an off-center underside position near an edge thereof; a transfer arm, with the electrostatic pick-up positioned near a first end and on an upper surface thereof; and drive means for rotating the transfer arm in the theta axis, and thereby swing the electrostatic pick-up through an arc, or for vertically moving the transfer arm and electrostatic pick-up in the z-axis. The electrostatic chuck is preferably a bipolar electrostatic pick-up and is preferably comprised of either a ceramic based material or polyamide. The electrostatic chuck may be connected to a power source by inductive coupling. The drive means may include a drive shaft connected to a second end of the transfer arm; a vertical actuator connected to the drive shaft for providing movement in the z-axis; a magnetic rotary actuator connected to the drive shaft for providing movement in the theta axis; and a rotatable bellows assembly surrounding the drive shaft and separating atmosphere within the bellows assembly from an external vacuum environment. The vertical actuator may be either an air actuator, or an electro-mechanical actuator coupled to a lead screw on the drive shaft. Alternatively, the drive means may include a drive shaft connected to a second end of the transfer arm; an actuator connected to said drive shaft for providing linear movement in the z-axis and rotary movement in the theta axis; and a bellows assembly, with a sealed rotary connection therethrough, surrounding said drive shaft and separating atmosphere within the bellows assembly from an external vacuum environment.
According to another aspect of the invention, provided is an apparatus for processing semiconductor wafers comprising a central transfer chamber having a wafer transfer robot therein for transferring wafers on a processing plane; a plurality of process chambers surrounding and connected to the central transfer chamber on the processing plane; a pre/post processing chamber located above the transfer chamber on a pre/post processing plane; and a wafer transfer device for engaging the semiconductor wafer at an off-center position and transferring the wafer between the robot in the processing plane and the pre/post processing chamber in the pre/post processing plane. The wafer transfer device may include a bipolar electrostatic pick-up for engaging the semiconductor wafer at an off-center position near an edge thereof; a transfer arm, with the electrostatic pick-up being positioned near a first end and on an upper surface thereof; and drive means for rotating the transfer arm and electrostatic pick-up in the theta axis, or vertically moving the transfer arm and electrostatic pick-up in the z-axis.
A third aspect of the present invention is a method for transferring an article, i.e. a semiconductor wafer, both in a z-axis and a theta axis. The method according to this aspect of the invention comprises the steps of engaging the article with an electrostatic pick-up at an off-center position near an edge thereof; rotating a transfer arm carrying said electrostatic pick-up in the theta axis; and vertically moving the article carried by the transfer arm and electrostatic pick-up in the z-axis. The step of vertically moving the article may include raising the article from a processing plane to a pre/post processing plane. Furthermore, the step of engaging the article may include positioning the electrostatic pick-up below the article; rotating the transfer arm to position the electrostatic pick-up at a point below and off-center of the article; raising the electrostatic pick-up to contact a lower surface of the article at an off-center position near the edge thereof; and energizing the electrostatic pick-up to create an attraction force on the article. The article is preferably a semiconductor wafer, which may be transferred from an end effector located within a vacuum chamber to a pre/post processing chamber located above the vacuum chamber.
These and other features, aspects and advantages of the present invention will become better understood by referring to the following detailed description, drawings and claims, wherein examples of the presently preferred embodiments are given for purposes of illustration and disclosure.